Traditional optical fiber transport devices 200a and 200b are shown in FIG. 53. A pair of the optical transport devices 200a and 200b are connected by an optical fiber 204 each another. The optical transport device 200a transmits an optical signal 205 of wavelength λ1, where the optical transport device 200b transmits an optical signal 206 of wavelength λ2. The wavelengths of upstream and downstream optical signals comprise different wavelengths so that a full-duplex optical communication channel is established over a single fiber.
An optical transport device 200a comprises an optical transceiver 201a, an optical amplifier 202a, and a wavelength division multiplexer 203a. The optical transceiver 201a transmits an optical signal 205 of wavelength λ1. The wavelength multiplexer 203a multiplexes optical signals of wavelengths λ1 and λ2.
An optical transport device 200b comprises an optical transceiver 201b, an optical amplifier 202b, and a wavelength division multiplexer 203b. The optical transceiver 201b transmits an optical signal 206 of wavelength λ2. The wavelength multiplexer 203b multiplexes optical signals of wavelengths λ1 and λ2.
The optical amplifiers 202a and 202b are boost amplifiers that amplify transmission signals. There is another application, an optical pre-amplifier that amplifies an optical receiving signal, is less popular than the boost amplifier. There is the other application that uses both of the boost amplifier and pre-amplifier. This application is not popular.